//
// This code was created by Jeff Molofee '99 (ported to Linux/GLUT by Richard Campbell '99)
//
// If you've found this code useful, please let me know.
//
// Visit me at www.demonews.com/hosted/nehe 
// (email Richard Campbell at ulmont@bellsouth.net)
//
#include <GL/glut.h>// Header File For The GLUT Library 
#include <GL/gl.h>	// Header File For The OpenGL32 Library
#include <GL/glx.h> // Header File For The Glx Library
#include <GL/glu.h>	// Header File For The GLu32 Library
#include <unistd.h> // Header File For sleeping
#include <stdio.h>	// Header File For printf Debugging
#include <math.h>	// Header File For sin/cos Functions
#include <string.h>	// Header File For strlen Function

/* ascii code for the escape key */
#define ESCAPE 27

/* The number of our GLUT window */
int window; 

GLuint base; //绘制字体的显示列表的开始位置
GLfloat cnt1;	//字体移动计数器1
GLfloat cnt2;	//字体移动计数器2

GLvoid BuildFont(GLvoid)
{
	Display *dpy;
	XFontStruct *fontInfo;//存储字体 

	base = glGenLists(96);//用来存储96个字符

	//加载字体。 你所拥有的字体的种类是依赖你的系统，在我的系统上，字体信息在/etc/X11/fonts文件夹下
	//得到当前显示器。这个操作在显示器环境中打开了第二个到显示器的连接，它将持续足够长来加载字体
	dpy = XOpenDisplay(NULL);//默认的显示器环境

	fontInfo = XLoadQueryFont(dpy, "-adobe-helvetica-medium-r-normal--18-*-*-*-p-*-iso8859-1");
	if (fontInfo == NULL)
	{
		fontInfo = XLoadQueryFont(dpy, "fixed");
		if (fontInfo == NULL)
		{
			printf("No X font available?\n");
		}
	}

	//加载字体信息以后，现在是最好的时机来旋转、绽放或是冷却字体
	//以32号字体（空格）开始，共96个字符，将它们存在以base的起始处
	glXUseXFont(fontInfo->fid, 32, 96, base);

	//释放我们得到的字体，因为我们已经得到显示列表
	XFreeFont(dpy, fontInfo);

	//关闭第二个连接
	XCloseDisplay(dpy);
}

//删除字体
GLvoid KillFont(GLvoid) 
{
	glDeleteLists(base, 96);//删除所有的96个字符
}

GLvoid glPrint(char *text)//传统的gl输入方式
{
	if (text == NULL)//如果没有内容要输出，什么也不做
	{
		return;
	}

	glPushAttrib(GL_LIST_BIT);//// 把显示列表属性压入属性堆栈
	glListBase(base - 32);//将初始字符设为32
	glCallLists(strlen(text), GL_UNSIGNED_BYTE, text);//绘制显示列表文字
	glPopAttrib();//恢复GL_LIST_BIT属性

}

/* A general OpenGL initialization function.  Sets all of the initial parameters. */
void InitGL(int Width, int Height)	        // We call this right after our OpenGL window is created.
{
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);		// This Will Clear The Background Color To Black
    glClearDepth(1.0);				// Enables Clearing Of The Depth Buffer
    glDepthFunc(GL_LESS);				// The Type Of Depth Test To Do
    glEnable(GL_DEPTH_TEST);			// Enables Depth Testing
    glShadeModel(GL_SMOOTH);			// Enables Smooth Color Shading

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();				// Reset The Projection Matrix

    gluPerspective(45.0f,(GLfloat)Width/(GLfloat)Height,0.1f,100.0f);	// Calculate The Aspect Ratio Of The Window

    glMatrixMode(GL_MODELVIEW);

	BuildFont();//构建字体
}

/* The function called when our window is resized (which shouldn't happen, because we're fullscreen) */
void ReSizeGLScene(int Width, int Height)
{
    if (Height==0)				// Prevent A Divide By Zero If The Window Is Too Small
        Height=1;

    glViewport(0, 0, Width, Height);		// Reset The Current Viewport And Perspective Transformation

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    gluPerspective(45.0f,(GLfloat)Width/(GLfloat)Height,0.1f,100.0f);
    glMatrixMode(GL_MODELVIEW);
}

/* The main drawing function. */
void DrawGLScene()
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);		// Clear The Screen And The Depth Buffer
    glLoadIdentity();				// Reset The View
    glTranslatef(0.0f, 0.0f, -1.0f);

	//根据文字位置附着颜色
	glColor3f(1.0f*((float)(cos(cnt1))), 1.0f*((float)(sin(cnt2))), 1.0f-0.5f*((float)(cos(cnt1+cnt2))));

	//字符在显示屏上的位置
	glRasterPos2f(-0.2f+0.35f*((float)(cos(cnt1))), 0.35f*((float)(sin(cnt2))));

	glPrint("OpenGL With NeHe");//打印gl文字到屏幕

	cnt1 += 0.01f;
	cnt2 += 0.0081f;
    // since this is double buffered, swap the buffers to display what just got drawn.
    glutSwapBuffers();
}

/* The function called whenever a key is pressed. */
void keyPressed(unsigned char key, int x, int y) 
{
    /* avoid thrashing this procedure */
    usleep(100);

    /* If escape is pressed, kill everything. */
    if (key == ESCAPE) 
    { 
        /* shut down our window */
        glutDestroyWindow(window); 

        /* exit the program...normal termination. */
        exit(0);                   
    }
}

int main(int argc, char **argv) 
{  
    /* Initialize GLUT state - glut will take any command line arguments that pertain to it or 
       X Windows - look at its documentation at http://reality.sgi.com/mjk/spec3/spec3.html */  
    glutInit(&argc, argv);  

    /* Select type of Display mode:   
       Double buffer 
       RGBA color
       Alpha components supported 
       Depth buffer */  
    glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_ALPHA | GLUT_DEPTH);  

    /* get a 640 x 480 window */
    glutInitWindowSize(640, 480);  

    /* the window starts at the upper left corner of the screen */
    glutInitWindowPosition(0, 0);  

    /* Open a window */  
    window = glutCreateWindow("Jeff Molofee's GL Code Tutorial ... NeHe '99");  

    /* Register the function to do all our OpenGL drawing. */
    glutDisplayFunc(&DrawGLScene);  

    /* Go fullscreen.  This is as soon as possible. */
    glutFullScreen();

    /* Even if there are no events, redraw our gl scene. */
    glutIdleFunc(&DrawGLScene);

    /* Register the function called when our window is resized. */
    glutReshapeFunc(&ReSizeGLScene);

    /* Register the function called when the keyboard is pressed. */
    glutKeyboardFunc(&keyPressed);

    /* Initialize our window. */
    InitGL(640, 480);

    /* Start Event Processing Engine */  
    glutMainLoop();  

    return 1;
}

